Body $A$ of mass $4m$ moving with speed $u$ collides with another body $B$ of mass $2m$, at rest. The collision is head on and elastic in nature. After the collision the fraction of energy lost by the colliding body $A$ is:

1. A
   $\frac{1}{9}$
2. B
   $\frac{8}{9}$
3. C
   $\frac{4}{9}$
4. D
   $\frac{5}{9}$